1. Field of the Invention
Embodiments of the present invention generally relate to orthopaedic implants and, more specifically, to identification of blind landmarks on orthopaedic implants.
2. Related Art
The interlocking femoral nail has significantly widened the scope for intramedullary (IM) fixation of long bone fractures. Locking an IM nail makes the construct more stable longitudinally and stops rotation of the nail within the bone. A typical IM nail fixation surgery involves a combination of jigs, x-ray imaging, and manual “eye-balling” to locate and drill the distal screw holes.
In this surgical procedure, an IM nail is hammered into the canal of a fractured long bone in order to fixate the fractured ends together. Typically, the proximal locking is performed first and is usually carried out with a jig. Nail deformation during intramedullary insertion, however, may make a jig inaccurate for the distal screws. The primary difficulty lies in the positioning of the distal locking screws and alignment of the drill for the drilling of the distal screw holes because it is the most time consuming and challenging step of the overall implantation procedure. Consequently, the two main reasons for failure in distal locking are incorrect entry point on the bone and wrong orientation of the drill. If either of these two factors is wrong, then the drill will not go through the nail hole.
An inaccurate entry point also compounds the problem as the rounded end of the drill bit often slips, and it is then difficult to place another drill hole next to the earlier one. Inaccurate distal locking may lead to premature failure with breakage of the nail through the nail hole, breakage of the screw, or the breaking of the drill bit within the bone.
Manual techniques are the most common and accepted techniques for sighting the distal screw holes and predominate the orthopaedic industry. The majority of distal targeting techniques employ a bushing (cylindrical sleeve) that guides the drill. The mechanism of aligning the guide bushing and keeping it in place differs. There are cases where the surgeons use a half sleeve (bushing cut in half longitudinally) or a full sleeve to help steady the drill bit during drilling In either situation, the surgeon will incise the patient and insert the drill through the incision. The manual techniques are based primarily on the surgeon's manual skill and make use of radiographic x-ray imaging and mechanical jigs.
Another method for achieving this on long nails is by using a technique called “perfect circles” with the aid of a C-arm. This is where one orients the patient and the C-arm such that when viewing the implant fluoroscopically the hole with which the screw is to pass appears to be in the shape of a circle. If the C-arm is not perpendicular to the hole then it would appear oblong or even absent.
There remains a need in the art for a system and method for targeting landmarks of a medical implant. Further, there remains a need in the art for accurately positioning the distal locking screws and aligning the drill for the drilling of the distal screw holes.